Showing papers on "Chemical state published in 1974"

Chemical Shifts in Photo-Excited Auger Spectra

Abstract: The energies of the LMM Auger transitions show, for certain elements, a far greater dependence on chemical state than do the binding energies of the individual electrons involved in the transitions. This behaviour is not predicted by the existing models for the energy of an Auger transition but is of considerable practical importance in the examination of surface films by X.p.s. It permits, for example, the separation of the photo-excited spectrum due to a surface oxide from that of an underlying metal where this would be impossible by using photoelectrons alone. In this paper we describe the determination of such chemical shifts by the in situ oxidation of evaporated metals in the range iron to selenium. The self-consistency of the body of data thus obtained was checked by the determination of the energies of the excited 3d and 3p states occurring during the LMM transitions. This form of examination also permitted determination of the 'effective incremental charge', as postulated in the model of Bergstrom & Hill (1954), for both the metals and their oxides. This parameter depended very strongly and in a nonlinear way on chemical state. The nonlinearity is accounted for by use of a new model which retains the simplicity of that due to Bergstrom & Hill but allows the inclusion of polarization and ionic charge effects. In such a sequence of oxides, which have known oxygen densities, the O 1s peak provides an excellent standard against which the intensities of the Auger signals can be compared: it is found that the relative intensity increases linearly from nickel through to arsenic.

Structure of catalysts: Determination by EPR and Fourier analysis of the extended x-ray absorption fine structure

Abstract: An alumina‐supported CuCr catalyst was examined with the extended x‐ray absorption fine‐structure (EXAFS) technique. This is a new technique which can determine the chemical states and near‐neighbor environments of the separate Cu and Cr atomic species. Cu was found to occupy both tetrahedral and octahedral sites in the supporting alumina lattice while Cr was found only in octahedral sites. The valence state was Cr+5 in the fresh catalyst which changed to Cr+6 in the exhaust‐cycled material. Confirmation of the valence state assignment was obtained by EPR. Fourier analysis of the EXAFS produced separate radial structure functions for the Cu and Cr atoms since the experiment measures the properties of the individual atomic species rather than those of the structure as a whole. Significant differences were observed by both techniques between fresh and exhaust‐cycled material.

Chemical State Analyses of Sulfur, Chromium and Tin by High Resolution X-Ray Spectrometry

Abstract: Chemical shifts of SKα, CrKβ1,3 and SnLβ2 were precisely measured with a two-crystal X-ray spectrometer (Toshiba AFV 701). Sulfur in the coke for iron smelting takes two oxidation states, i.e., S2− and S6+. Quantitative analyses of S2− and S6+ were performed by precisely measuring the profile of SKα and fitting the standard S2− of S6+ curve to the observed SKα profile with the non-linear least square method. Chemical shifts of CrKβ1,3 and SnLβ2 were utilized for the determinations of Cr6+, Cr3+, Sn4+ and Sn2+ in electro-plating solutions. Intensity ratio of IA to Ig was measured, where B means the point which showed an intensity independent of oxidation states. A means the point which showed the most dependent. Linear relations were found between intensity ratio IA/IB and Cr3+/Cr or Sn2+/Sn.

Studies on the chemical and colloidal nature of Pu(IV) polymer

Abstract: From tweniy-fourth congress of the International Union of Pure and Applied Chemistry; Hamburg, F. R. Germany (3 Sep 1973). Spectrophotometric, x- ray, electron diffraction, and electron microscopy studies of plutonium polymer are reported. Results indicate that the polymer consists of very small discrete particles, which can be either amorphous or crystalline, and which can be colloidally dispersed in a suitable medium such as ddlute HCl or HNO/sub 3/. Results also indicate that a monomeric Pu(IV) hydroxide species is not formed during initial precipitation as has been previously reported, but instead small crystallites of hydrated PuO/sub 2/. (JGB)